Gg. Kochendoerfer et al., ULTRAVIOLET RESONANCE RAMAN EXAMINATION OF THE LIGHT-INDUCED PROTEIN STRUCTURAL-CHANGES IN RHODOPSIN ACTIVATION, Biochemistry, 36(43), 1997, pp. 13153-13159
Ultraviolet resonance Raman (UVRR) spectra of rhodopsin and its metarh
odopsin I and metarhodopsin II photointermediates have been obtained t
o examine the molecular mechanism of G-protein-coupled receptor activa
tion. Spectra were acquired using a single-pass capillary flow techniq
ue in combination with a Littrow prism UV prefilter detection system.
The UVRR difference spectra between rhodopsin and metarhodopsin I exhi
bit small differences assignable to tyrosine residues and no differenc
es due to tryptophan. The UVRR difference spectra between rhodopsin an
d metarhodopsin II exhibit significant differences for vibrations of b
oth tryptophan and tyrosine residues. Most importantly, there is an in
tensity decrease of the totally symmetric tryptophan modes at 759, 100
8, and 1545 cm(-1), an intensity decrease of the tryptophan W7 band at
1357 cm(-1), and a frequency shift of the tryptophan W17 band from 88
5 to 892 cm(-1) These difference features are assigned to one or more
tryptophan residues that reside in a hydrophobic, weakly hydrogen-bond
ing environment in rhodopsin and that are transferred to a less hydrop
hobic, non-hydrogen-bonding environment during rhodopsin activation. T
he available evidence suggests that Trp(265) makes a dominant contribu
tion to the tryptophan features in this difference spectrum. These res
ults are interpreted with a model for rhodopsin activation in which re
tinal isomerization alters the interaction of Trp(265) With the ionone
ring of the retinal chromophore.